1. DNA can form many structures!
The Many Forms of DNA
DNA can form many structures!

2. I. Organization of Genetic Material
Each human cell has about 6.5 feet of DNA
→enough DNA in your whole body to go to the sun and back 500 times!
→ Question: How can you store all that DNA in your cells?

3. DNA can form many structures, and they all have different names!
–––––– Chromatin
DNA can form many structures, and they all have different names!

4. I. Organization of Genetic Material
Chromatin: The form of DNA when it is NOT visible to the human eye
Chromosome: The form of DNA when it is tightly coiled around histone proteins and is visible to the human eye.

5. I. Organization of Genetic Material
What are genes?

6. I. Organization of Genetic Material
A gene is a section of DNA that makes 1 protein.
Alleles are different versions of the same gene.
Gene for eye color proteins
Gene for hair color proteins

7. I. Organization of Genetic Material
Human Chromosome #20

8. E. How are chromosomes organized in the cell?
I. Organization of Genetic Material
E. How are chromosomes organized in the cell?
Chromosomes come in pairs.

9. Chromosomes come in HOMOLOGOUS PAIRS
I. Organization of Genetic Material
Chromosomes come in HOMOLOGOUS PAIRS
matching
This is true for all organisms that have 2 parents… No matter what– a mouse, a fly, etc.
Half of the chromosomes come from the FATHER.
The other matching half comes from the MOTHER.

10. I. Organization of Genetic Material
Gametes (sex cells: sperm or egg)
Human gametes only have 23 chromosomes (no pairs!
That’s half the DNA you have in all your other cells!

11. Why only HALF the chromosomes in gametes??
I. Organization of Genetic Material
Why only HALF the chromosomes in gametes??
Think about it…

12. Imagine a human sperm and egg cell with full DNA coming together…
I. Organization of Genetic Material
Imagine a human sperm and egg cell with full DNA coming together… 46
Sperm (male sex cell) from Dad 46
Egg (female sex cell) from Mom 92
Baby’s first Body Cell (“Zygote”)

13. Now, imagine a sperm and egg cell with half DNA coming together…
I. Organization of Genetic Material
Now, imagine a sperm and egg cell with half DNA coming together… 23
Sperm (male gamete) from Dad 23
Egg (female gamete) from Mom 46
Baby’s first Body Cell (“Zygote”)

14. How do the sex cells get only half the number of chromosomes???
MEIOSIS!

15. DIPLOID (2n)= full set of chromosomes—1 from mom, one from dad
I. Organization of Genetic Material
Diploid v. Haploid:
All organisms have a certain number of chromosomes in their SOMATIC (body) cells called the diploid number.
DIPLOID (2n)= full set of chromosomes—1 from mom, one from dad
Organism
Diploid Number
Human
46 (23 pairs)
Corn
20 (10 pairs)
Dog
78 (39 pairs)
Chicken
Crayfish
200 (100 pairs)

16. HAPLOID (1n)= half set of chromosomes
I. Organization of Genetic Material
Diploid v. Haploid:
All organisms only have half the number of chromosomes in their GAMETES (sex cells) called the haploid chromosome number.
HAPLOID (1n)= half set of chromosomes
Organism
Diploid Number
Haploid Number
Human 46 23
Corn 20 10
Dog 78 39
Chicken
Crayfish
200
100

17. Quick Check!
When DNA is tightly wrapped around proteins it is called a _____________.
A section of DNA that makes one protein is called a ___________.
Why do chromosomes come in homologous pairs?
T/F: All cells have a full set of DNA and are called “diploid.”
An elephant has 56 chromosomes. What is its haploid number (1n)?

18. Quick Check!
When DNA is tightly wrapped around proteins it is called a chromosome.
A section of DNA that makes one protein is called a gene.
Why do chromosomes come in homologous pairs?
T/F: All cells have a full set of DNA and are called “diploid.” FALSE
An elephant has 56 chromosomes. What is its haploid number (1n)? 28

19. How does a body make gametes?
Say “My-OH-sis”
Meiosis:
How does a body make gametes?

20. So…do all cells in the body have the same number of chromosomes?
Review: Pair and Share
How is DNA stored in a cell?
What is the difference between somatic (body) cells and gametes (sex) cells?
So…do all cells in the body have the same number of chromosomes?

21. SOMATIC CELLS (body cells) are DIPLOID (2n) = TWO full sets of chromosomes
Organism
Diploid Number
Human
46 (23 pairs)
Corn
20 (10 pairs)
Dog
78 (39 pairs)
Chicken
Crayfish
200 (100 pairs)
Adder’s Tongue
1260 (630 pairs)
Do you know where they get each set?

22. GAMETES (sex cells) are HAPLOID (1n) = ONE full set of chromosomes
Organism
Diploid Number
Haploid Number
Human 46 23
Corn 20 10
Dog 78 39
Chicken
Crayfish
200
100
Adder’s
1260
630

23. Gametes (sex cells) need to be haploid!
II. Meiosis Overview
Gametes (sex cells) need to be haploid! 23 23
Male Gamete (sperm)
Female Gamete (egg) 46
ZYGOTE

24. A. If your body needs a new somatic (body) cell…
II. Meiosis Overview
A. If your body needs a new somatic (body) cell…
How does that cell get made? (Hint: think of the cell cycle)
DNA Replication, then MITOSIS (one cell splits into two)

25. If your body needs a new gamete(sex cell)…
II. Meiosis Overview
If your body needs a new gamete(sex cell)…
How does that cell get made?
DNA replication, then MEIOSIS (one cell splits into four)

26. Compare and Contrast: Mitosis versus Meiosis
II. Meiosis Overview
Compare and Contrast: Mitosis versus Meiosis

27. III. Stages of Meiosis 0. INTERPHASE (Pre-Meiosis)
Cell does DNA replication
*NOTE* Meiosis ONLY happens in the OVARIES & TESTES (sex organs)
Homologous pair
Another homologous pair

28. III. Stages of Meiosis A closer look… INTERPHASE “sister chromatids”
Still homologous pairs, there’s just a copy of each now!
Q: What is similar about these sister chromatids?

29. III. Stages of Meiosis 1. Prophase 1
centrioles
Chromosomes condense and become visible
Homologous chromosomes come together and Pair up
Crossing over occurs ***
Nuclear membrane disappears
Spindle fibers form from centrioles and will attach to sister chromatids at their centromeres !

30. III. Stages of Meiosis 2. Metaphase 1
Spindles move the homologous pairs toward the Middle

31. III. Stages of Meiosis 3. Anaphase 1
Homologous pairs get pulled Apart to opposite sides with the shortening of the spindle fibers

32. 4. Telophase 1 (and Cytokinesis)
III. Stages of Meiosis
4. Telophase 1 (and Cytokinesis)
The cell splits into Two cells
Other things going on:
Nuclear membrane starts to form again
Spindles disappear
Period 5 – No cool down and no PMAT

33. WOW! We just made 1 cell split into 2…
How will you remember all those phases?
Prophase
Metaphase
Anaphase
Telophase
How will we make 4 cells???
Paco
Made
Estoy haciendo
un taco.
Paco A
Taco

34. To make gametes, the cells in our sex organs repeat P-M-A-T!
Going through P-M-A-T two times will complete the meiosis process.
Let’s continue…

35. III. Stages of Meiosis 5. Prophase 2
Chromosomes condense and become visible
Both cells Prepare to split again
No crossing over
Nuclear membrane disappears again
Spindle fibers form again and attach to centromeres

36. III. Stages of Meiosis 6. Metaphase 2
Sister chromatids line up in the Middle

37. III. Stages of Meiosis 7. Anaphase 2
Sister chromatids get pulled Apart to opposite ends as spindle fibers shorten

38. 8. Telophase 2 (and cytokinesis)
III. Stages of Meiosis
8. Telophase 2 (and cytokinesis)
Each cell splits into Two cells-- totaling 4 haploid cells
Other things going on:
Nuclear membrane appears again
Spindles disappear

39. Result: Now we have 4 HAPLOID cells!

40. QUICK CHECK!
How does the original parent cell compare to the daughter cells in:
Chromosome number?
Genetic information in chromosomes?

41. The BIG FINISH
Identify 3 differences between MITOSIS and MEIOSIS.

42. MITOSIS (making SOMATIC cells) MEIOSIS (making GAMETES)
The BIG PICTURE
Work with a partner to fill in the chart below…
MITOSIS (making SOMATIC cells)
MEIOSIS (making GAMETES)
Number of cells at start 1
How many times does DNA replication happen?
How many times does the cell divide its nucleus?
How many cells at the end?
Are the cells DIPLOID or HAPLOID?

43. MITOSIS (making SOMATIC cells) MEIOSIS (making GAMETES)
The BIG PICTURE
Work with a partner to fill in the chart below…
MITOSIS (making SOMATIC cells)
MEIOSIS (making GAMETES)
Number of cells at start 1
How many times does DNA replication happen?
How many times does the cell divide its nucleus? 2
How many cells at the end? 4
Are the cells DIPLOID or HAPLOID?
DIPLOID
HAPLOID